This is not a simple question to answer as there are many variables; but the simple answer is that the probability of recording a better image exists with the APS camera.
With the SX50 you have a 5.6x crop of a 215mm lens' image circle. And with the APS you have a 4x crop of a 300mm lens' image circle; which means the APS retains more of the light from the scene/image... advantage to the APS.
At 215mm the SX50 lens is at f/6.3 and projects details at a minimum average size of approx. 9microns, which is approximately 6x the size of a pixel on that sensor (1.5um)... but that's only if the lens were optically perfect, and that lens most certainly is not. Best case (theoretical) scenario is ~ .35MP average of recorded resolution w/ a lower contrast level... reality is probably notably worse.
With the APS there is the potential of using a faster and better lens, lets say a 300/2.8. At f/2.8 a lens projects details at an average minimum size of 3.8 microns. Or say a 300/4 which will project details at an average minimum size of 5.4 microns. Both would fit within the size of a pixel of most APS cameras (or w/in the diffraction limit of 2x). E.g. the D7500 has 4.2 micron pixels and ~ 8 micron diffraction limit. Best case (theoretical) scenario, ~ 2.5MP recorded resolution with a much higher level of contrast... advantage to the APS again.
Edit: even the 70-300vr would be at f/5.6-300mm and could project details at an average minimum of 7.5 microns, less that the D7500 diffraction limit (again theoretical, the lens probably isn't that good wide open).
Then there is the consideration of motion (camera shake/subject/atmospheric/etc)... and again, the larger pixel size on the larger APS sensor gives a potential increase in actual recorded resolution because a detail can move much farther before crossing an equivalent number of pixels.